The present invention relates to rotary fluid pressure devices of the type in which a gerotor gear set typically serves as the fluid displacement mechanism, and more particularly, to such devices which are provided with multiple-speed (multiple-displacement) capability. Furthermore, the present invention relates to an improved method for controlling the shifting (between different speeds) of such a multiple-speed device.
Although the teachings of the present invention can be applied advantageously to devices having fluid displacement mechanisms other than gerotor gear sets (such as radial piston and cam lobe type devices), the present invention is especially adapted for use with devices utilizing gerotor gear sets, and will be described in connection therewith. Furthermore, the present invention is especially adapted for devices to be utilized as motors, and will be described in connection therewith.
Motors utilizing gerotor gear sets can be used in a variety of applications, one of the more common applications being vehicle propulsion, wherein the vehicle includes an engine driven pump which provides pressurized fluid to a vehicle hydraulic propel circuit, including a pair of gerotor motors, with each motor being associated with one of the drive wheels. Those skilled in the art will understand that many gerotor motors utilize a roller gerotor gear set, especially on larger, higher torque motors of the type typically used in propel applications, and subsequent references hereinafter to a xe2x80x9cgerotorxe2x80x9d will be understood to mean and include both a conventional gerotor as well as a roller gerotor, and for purposes of this invention, xe2x80x9cgerotorxe2x80x9d can include either an IGR (internally-generated rotor) or and EGR (externally-generated rotor), both of which are now generally well known to those skilled in the art.
Multiple-speed gerotor motors are known from U.S. Pat. Nos. 4,480,971; 6,068,460; and 6,099,280, all of which are assigned to the assignee of the present invention and incorporated herein by reference. The device of the ""971 patent has been in widespread commercial use and has performed in a generally satisfactory manner, and more recently, the devices of the ""460 and ""280 patents have also come into commercial usage. As is now well know to those skilled in the art, a gerotor motor may be operated as a multiple-speed (multiple displacement) device by providing valving which can effectively xe2x80x9crecirculatexe2x80x9d fluid between expanding and contracting fluid volume chambers of the gerotor gear set. If the inlet port communicates with all of the expanding volume chambers, and all of the contracting volume chambers communicate with the outlet port, the motor operates in the normal, low-speed, high-torque (LSHT) mode. If some of the fluid from certain of the contracting volume chambers (the xe2x80x9crecirculatingxe2x80x9d chambers) is recirculated back to the expanding volume chambers, the result will be operation in a high-speed, low-torque (HSLT) mode. The HSLT mode yields the same result as if the displacement of the gerotor were decreased, but with the same fluid flow rate through the gerotor.
The multiple-speed gerotor motors, made in accordance with the above-incorporated patents, and sold commercially by the assignee of the present invention, operate very satisfactorily in both the LSHT and the HSLT modes. It has been observed, however, that when the motor is shifted from one mode to the other (and especially, from the HSLT mode to the LSHT mode), there is a tendency for cavitation to occur in the gerotor gear set just as the shift is occurring from one mode to the other. During the shift from HSLT to LSHT, the xe2x80x9cdisplacementxe2x80x9d of the motor increases, while the speed of the vehicle and the pump flow remain, at least in the short term, generally constant. Thus, the gerotor gear set is suddenly being xe2x80x9cdisplacedxe2x80x9d at a speed corresponding to an instantaneous fluid flow rate which is greater than what the pump can immediately provide.
The recirculating fluid volume chambers have the greatest tendency to cavitate because of greater restriction in the recirculation flow path than in the flow paths to and from those volume chambers which don""t recirculate. As is well know to those skilled in the art, cavitation occurring within a fluid displacement element, such as a gerotor, causes a substantial amount of undesirable noise, and can also eventually result in damage to the displacement mechanism. Typically, the cavitation will continue until the vehicle slows down to a speed at which the pump flow xe2x80x9ccatches up withxe2x80x9d the speed (displacement) of the gerotor gear set in the motor.
Accordingly, it is an object of the present invention to provide an improved fluid pressure operated device having multiple-speed capability, in which shifting from one mode to another does not result in any substantial amount of cavitation and noise.
It is a more specific object of the present invention to provide an improved method for controlling the shifting of a multiple-speed fluid pressure operated device, wherein the shifting occurs without any substantial amount of cavitation and noise.
The above and other objects of the invention are accomplished by the provision of an improved fluid pressure operated device comprising housing means defining a fluid inlet port and a fluid outlet port. A fluid pressure displacement mechanism is associated with the housing means and includes an internally toothed ring member and an externally toothed star member eccentrically disposed within the ring member, the ring member and the star member having relative orbital and rotational movement, and interengaging to define a plurality N of expanding and contracting fluid volume chambers in response to the orbital and rotational movement. A motor valve means cooperates with the housing means to provide fluid communication between the fluid inlet port and the expanding volume chambers, and between the contracting volume chambers and the fluid outlet port in a normal, low-speed, high-torque mode of operation. A shift valve means is operable, in a first condition, to permit the normal low-speed, high-torque mode of operation and, in a second condition, to interconnect a plurality M of the volume chambers, the plurality M comprising recirculating volume chambers.
The improved fluid pressure operated device is characterized by the device defining a supplemental fluid passage operable to provide fluid communication from a source of pressurized fluid to each of the plurality M of recirculating volume chambers. A control valve means is operable, in a normal mode, to block fluid communication from the source of pressurized fluid to the supplemental fluid passage and in a shift mode, to permit fluid communication from the source of pressurized fluid to the supplemental fluid passage.
In accordance with another aspect of the present invention, there is provided an improved method of controlling the shifting of a multiple-speed fluid pressure operated device from a first speed ratio to a second speed ratio, the device comprising housing means and a fluid pressure displacement mechanism as described previously. A motor valve means cooperates with the housing means to provide fluid communication in the normal manner in the first speed ratio. A shift valve means is operable in a first condition to achieve the first speed ratio, and in a second condition, to achieve the second speed ratio by interconnecting a plurality M of the volume chambers as recirculating volume chambers.
The improved method of controlling the shifting comprises the steps of providing a source of pressurized fluid and a supplemental fluid passage, operable to provide fluid communication from the source to each of the plurality M of recirculating volume chambers. The next step is changing the shift valve means from the first condition to the second condition, and then sensing the changing of the shift valve means and only while the changing is being sensed, generating a change sense signal. The final step is detecting the change sense signal, and in response thereto, permitting fluid communication from the source of pressurized fluid, through the supplemental fluid passage, to the plurality M of recirculating volume chambers.